Molybdenum-modified vanadium-phosphorus oxide catalysts for the production of maleic anhydride

An active catalyst having a crystal structure corresponding to that of a catalyst that has been prepared and activated by the following process. A substantially pentavalent vanadium-containing compound is reacted with a pentavalent phosphorus-containing compound in an alcohol medium capable of reducing the vanadium to an oxidation state of less than +5. Molybdenum is incorporated into the product of the reaction, thereby forming a solid molybdenum-modified precursor composition. The alcohol is removed to produce a dried solid molybdenum-modified precursor composition. Shaped bodies comprising said dried solid molybdenum-modified precursor composition are formed. The dried formed molybdenum-modified catalyst precursor composition is activated to transform it into the active catalyst.

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Claims

1. An active, phosphorus vanadium oxide catalyst for the conversion to maleic anhydride of a non-aromatic hydrocarbon having at least four carbon atoms in a straight chain, said catalyst comprising a shaped body having a volume of at least about 0.02 cc and a B.E.T. surface area of at least about 15 m.sup.2 /g, and said catalyst containing molybdenum and having a molar ratio of molybdenum to vanadium of between about 0.0020 and about 0.0060.

2. An active catalyst as set forth in claim 1 wherein said molybdenum of said catalyst has an oxidation state of 6+.

3. An active catalyst as set forth in claim 1 having an X-ray diffraction pattern wherein the ratio of the peak height at a d-spacing of about 3.86 angstrom to the peak height at a d-spacing of about 3.14 angstrom is between about 0.8 and about 1.3.

4. An active catalyst for conversion to maleic anhydride of a non-aromatic hydrocarbon having at least four carbon atoms in a straight chain, the catalyst comprising phosphorus, vanadium, oxygen, and molybdenum and having a macrostructure predominantly consisting of radially oriented three-dimensional networks of randomly shaped open cells, the molybdenum being concentrated at the surfaces of the walls of said cells.

5. An active catalyst as set forth in claim 4 comprising a phosphorus vanadium oxide substantially homogeneously distributed throughout the walls of said cells.

6. A fixed catalyst bed adapted for the production of maleic anhydride by passage therethrough of a gas stream initially comprising a mixture of a nonaromatic hydrocarbon having at least four carbon atoms in a straight chain and an oxygen containing gas, said catalyst bed comprising

a first zone containing a phosphorus vanadium oxide catalyst substantially devoid of active sites comprising molybdenum; and
a second zone downstream of said first zone with respect to the flow of said gas stream, said second zone comprising a molybdenum-modified phosphorus vanadium oxide catalyst comprising active sites comprising molybdenum.

7. A catalyst bed as set forth in claim 6 wherein maleic anhydride and acrylic acid are produced as said gas stream passes through said catalyst bed, and said gas stream contacts the active catalyst for a time sufficient to eliminate at least about 20% of the acrylic acid from the gas stream.

8. A catalyst bed as set forth in claim 7 wherein from about 20% to about 70% of the acrylic acid is eliminated from the gas stream.

9. A catalyst bed as set forth in claim 7 wherein from about 35% to about 65% of the acrylic acid is eliminated from the gas stream.

10. A fixed catalyst bed adapted for the production of maleic anhydride by passage therethrough of a gas stream initially comprising a mixture of a nonaromatic hydrocarbon having at least four carbon atoms in a straight chain and an oxygen containing gas, said catalyst bed comprising a mixture of the active catalyst of claim 1 and a phosphorous vanadium oxide catalyst substantially devoid of active sites comprising molybdenum.

11. A catalyst bed as set forth in claim 10 wherein maleic anhydride and acrylic acid are produced as said gas stream passes through said catalyst bed, and said gas stream contacts the active catalyst for a time sufficient to eliminate at least about 20% of the acrylic acid from the gas stream.

12. A catalyst bed as set forth in claim 11 wherein from about 20% to about 70% of the acrylic acid is eliminated from the gas stream.

13. A catalyst bed as set forth in claim 11 wherein from about 35% to about 65% of the acrylic acid is eliminated from the gas stream.

14. An active catalyst having a crystal structure corresponding to that of a catalyst that has been prepared and activated by a process comprising the steps of:

blending a phosphorus vanadium oxide powder and a molybdenum-containing powder to form a molybdenum-modified catalyst precursor composition;
forming the molybdenum-modified catalyst precursor composition into shaped bodies, each of said shaped bodies having a volume of at least about 0.02 cc; and
activating the formed molybdenum-modified catalyst precursor composition to transform it into the active catalyst.

15. An active catalyst as set forth in claim 14 wherein the formed molybdenum-modified catalyst precursor composition is activated by the steps of:

(a) heating the formed molybdenum-modified catalyst precursor composition in an atmosphere selected from the group consisting of air, steam, inert gas, and mixtures thereof, to a temperature not to exceed 300.degree. C.;
(b) maintaining the formed molybdenum-modified catalyst precursor composition at the temperature of Step (g) and providing an atmosphere containing molecular oxygen, steam, and optionally an inert gas, the atmosphere being represented by the formula
(c) increasing the temperature of the formed molybdenum-modified catalyst precursor composition at a programmed rate of from about 2.degree. C./min to about 12.degree. C./min to a value effective to eliminate the water of hydration from the formed molybdenum-modified catalyst precursor composition;
(d) adjusting the temperature from Step (c) to a value greater than 350.degree. C., but less than 550.degree. C., and maintaining the adjusted temperature in the molecular oxygen/steam-containing atmosphere for a time effective to provide a vanadium oxidation state of from about +4.0 to about +4.5; and
(e) continuing to maintain the adjusted temperature in a nonoxidizing, steam-containing atmosphere for a time effective to complete the formed molybdenum-modified catalyst precursor composition to active catalyst transformation to yield the active catalyst.

16. An active catalyst as set forth in claim 14 wherein said active catalyst comprises a shaped body having a volume of at least about 0.02 cc, a phosphorus/vanadium atom ratio of from about 1.05 to about 1.20, a B.E.T. surface area of at least about 15 m.sup.2 /g, an average vanadium oxidation state of between about 4.06 and about 4.3, a total pore volume of at least about 0.15 cc/g, a normalized apparent shaped body density of between about 1.0 and about 2.0 g/cc, and a crush strength of at least about 4 pounds, at least about 20% of the pore volume of said catalyst being constituted of pores having a diameter between about 0.1 microns and about 3.3 microns, and at least about 40% of the pore volume being constituted of pores having a diameter of less than about 0.1 microns.

17. An active catalyst as set forth in claim 14 wherein said molybdenum-modified catalyst precursor composition corresponds to the formula:

18. A process for the preparation of an active catalyst comprising the steps of:

blending a phosphorus vanadium oxide powder and a molybdenum-containing powder to form a molybdenum-modified catalyst precursor composition;
forming the molybdenum-modified catalyst precursor composition into shaped bodies, each of said shaped bodies having a volume of at least about 0.02 cc; and
activating the formed molybdenum-modified catalyst precursor composition to transform it into the active catalyst.

19. A process as set forth in claim 18 wherein the formed molybdenum-modified catalyst precursor composition is activated by the steps of:

(a) heating the formed molybdenum-modified catalyst precursor composition in an atmosphere selected from the group consisting of air, steam, inert gas, and mixtures thereof, to a temperature not to exceed 300.degree. C.;
(b) maintaining the formed molybdenum-modified catalyst precursor composition at the temperature of Step (g) and providing an atmosphere containing molecular oxygen, steam, and optionally an inert gas, the atmosphere being represented by the formula
(c) increasing the temperature of the formed molybdenum-modified catalyst precursor composition at a programmed rate of from about 2.degree. C./min to about 12.degree. C./min to a value effective to eliminate the water of hydration from the formed molybdenum-modified catalyst precursor composition;
(d) adjusting the temperature from Step (c) to a value greater than 350.degree. C., but less than 550.degree. C., and maintaining the adjusted temperature in the molecular oxygen/steam-containing atmosphere for a time effective to provide a vanadium oxidation state of from about +4.0 to about +4.5; and
(e) continuing to maintain the adjusted temperature in a nonoxidizing, steam-containing atmosphere for a time effective to complete the formed molybdenum-modified catalyst precursor composition to active catalyst transformation to yield the active catalyst.

20. A fixed catalyst bed as set forth in claim 6 wherein said second zone comprises molybdenum active sites in a proportion sufficient to reduce the acrylic acid content of the gas stream exiting the catalyst bed as compared to the acrylic acid content of a gas stream leaving a catalyst bed all zones of which are entirely devoid of molybdenum active sites.

21. A fixed catalyst bed as set forth in claim 20 wherein said molybdenum-modified phosphorus vanadium oxide catalyst comprises a shaped body having a volume of at least about 0.02 cc and a B.E.T. surface area of at least about 15 m.sup.2 /g, said catalyst containing molybdenum in a molar ratio of molybdenum to vanadium of at least about 0.0020.

22. A fixed catalyst bed as set forth in claim 20 wherein the molybdenum-modified catalyst in said second zone contains molybdenum in a molar ratio to vanadium of at between about 0.0020 and about 0.0060.

23. A fixed catalyst bed as set forth in claim 6 wherein said molybdenum-modified phosphorus vanadium oxide catalyst is prepared by a process comprising:

reacting substantially pentavalent vanadium-containing compound with a pentavalent phosphorus-containing compound in an alcohol medium capable of reducing the vanadium to an oxidation state of less than +5;
incorporating molybdenum into the product of the reaction, thereby forming a solid molybdenum-modified precursor composition;
removing the alcohol to produce a dried solid molybdenum-modified precursor composition;
forming shaped bodies comprising said dried solid molybdenum-modified precursor composition; and
activating the dried formed molybdenum-modified catalyst precursor composition to transform it into the active catalyst.

24. An active catalyst having a crystal structure corresponding to that of a catalyst that has been prepared and activated by a process comprising:

preparing a slurry comprising a mixture containing a phosphorus-containing compound, a pentavalent vanadium-containing compound and an alcohol medium capable of reducing the vanadium to an oxidation state of less than +5;
heating said mixture such that said vanadium-containing compound is reduced by said alcohol and reacts with said phosphorus-containing compound in said slurry to form a solid vanadium/phosphorus oxide precursor composition comprising mixed oxides of vanadium and phosphorus;
cooling said mixture after formation of said solid vanadium/phosphorus oxide precursor composition;
introducing a source of molybdenum into the cooled mixture containing said solid vanadium/phosphorus oxide precursor composition, and heating a slurry containing molybdenum and said solid vanadium/phosphorus oxide precursor composition to effect incorporation of molybdenum and formation of a solid molybdenum-modified precursor composition;
removing the alcohol to produce a dried solid molybdenum-modified precursor composition;
forming shaped bodies comprising said dried solid molybdenum-modified precursor composition; and
activating the dried formed molybdenum-modified catalyst precursor composition to transform it into the active catalyst.

25. An active catalyst having a crystal structure corresponding to that of a catalyst that has been prepared and activated by a process comprising:

preparing a slurry comprising a mixture containing a phosphorus-containing compound, a pentavalent vanadium-containing compound and an alcohol medium capable of reducing the vanadium to an oxidation state of less than +5;
heating said mixture such that said vanadium-containing compound is reduced by said alcohol and reacts with said phosphorus-containing compound in said slurry to form a solid particulate vanadium/phosphorus oxide precursor composition comprising mixed oxides of vanadium and phosphorus;
removing a portion of said alcohol medium from said mixture after formation of said solid vanadium/phosphorus oxide precursor composition; and
after removal of said portion of said alcohol, introducing a source of molybdenum into the mixture containing said solid vanadium/phosphorus oxide precursor composition;
incorporating molybdenum into the particulate vanadium/phosphorus oxide precursor, thereby forming a molybdenum-modified precursor composition;
removing alcohol to produce a dried solid molybdenum-modified precursor composition;
forming shaped bodies comprising said dried solid molybdenum-modified precursor composition; and
activating the dried formed molybdenum-modified precursor composition to transform into the active catalyst.

26. An active catalyst having a crystal structure corresponding to that of a catalyst that has been prepared and activated by a process comprising:

reacting a substantially pentavalent vanadium-containing compound with a pentavalent phosphorus-containing compound in an alcohol medium capable of reducing the vanadium to an oxidation state of less than +5;
incorporating molybdenum into the product of the reaction, thereby forming a solid molybdenum-modified precursor composition;
removing the alcohol to produce a dried solid molybdenum-modified precursor composition;
forming shaped bodies comprising said dried solid molybdenum-modified precursor composition and a pore modification agent; and
activating the dried formed molybdenum-modified catalyst precursor composition to transform it into the active catalyst, said active catalyst comprising a shaped body having a volume of at least about 0.02 cc, a phosphorus/vanadium atom ratio from about 1.05 to about 1.20, a B.E.T. surface area of at least about 15 m.sup.2 /g, an average vanadium oxidation state between about 4.06 and about 4.3, a total pore volume of at least about 0.15 g/cc, a normalized apparent shaped body density between about 1.0 and about 2.0 g/cc, and a crush strength of at least about 4 pounds, at least 20% of the pore volume of said catalyst being constituted of pores having a pore diameter between about 0.1 microns and about 3.3 microns, and at least 40% of the pore volume being constituted of pores having a diameter of less than about 0.1 microns.

27. An active catalyst having a crystal structure corresponding to that of a catalyst that has been prepared and activated by a process comprising:

reacting a substantially pentavalent vanadium-containing compound with a pentavalent phosphorus-containing compound in an alcohol medium capable of reducing the vanadium to an oxidation state of less than +5;
incorporating molybdenum into the product of the reaction, thereby forming a solid molybdenum-modified precursor composition;
removing the alcohol to produce a dried solid molybdenum-modified precursor composition;
forming shaped bodies comprising said dried solid molybdenum-modified precursor composition and a pore modification agent; and
activating the dried formed molybdenum-modified catalyst precursor composition to transform it into the active catalyst, said active catalyst comprising a shaped body having a B.E.T. surface area of at least about 15 m.sup.2 /g, an average vanadium oxidation state between about 4.0 and about 4.5, a total pore volume of at least about 0.15 g/cc, a normalized apparent shaped body density between about 1.0 and about 2.0 g/cc, and a crush strength of at least about 4 pounds, at least 5% of the pore volume of said catalyst being constituted of pores having a pore diameter of at least about 0.8 microns, and at least 4% of the pore volume being constituted of pores having a diameter of at least about 10 microns.

28. A process for the preparation of an active catalyst, the process comprising the steps of:

preparing a slurry comprising a mixture containing a phosphorus-containing compound, a pentavalent vanadium-containing compound and an alcohol medium capable of reducing the vanadium to an oxidation state of less than +5;
heating said mixture such that said vanadium-containing compound is reduced by said alcohol and reacts with said phosphorus-containing compound in said slurry to form a solid vanadium/phosphorus oxide precursor composition comprising mixed oxides of vanadium and phosphorus;
cooling said mixture after formation of said solid vanadium/phosphorus oxide precursor composition;
introducing a source of molybdenum into the cooled mixture containing said solid vanadium/phosphorus oxide precursor composition, and heating a slurry containing molybdenum and said solid vanadium/phosphorus oxide precursor composition to effect incorporation of molybdenum and formation of a solid molybdenum-modified precursor composition;
removing the alcohol to produce a dried solid molybdenum-modified precursor composition;
forming shaped bodies comprising said dried solid molybdenum-modified precursor composition; and
activating the dried formed molybdenum-modified catalyst precursor composition to transform it into the active catalyst.

29. A process for the preparation of an active catalyst, the process comprising the steps of:

preparing a slurry comprising a mixture containing a phosphorus-containing compound, a pentavalent vanadium-containing compound and an alcohol medium capable of reducing the vanadium to an oxidation state of less than +5;
heating said mixture such that said vanadium-containing compound is reduced by said alcohol and reacts with said phosphorus-containing compound in said slurry to form a solid particulate vanadium/phosphorus oxide precursor composition comprising mixed oxides of vanadium and phosphorus;
removing a portion of said alcohol medium from said mixture after formation of said solid vanadium/phosphorus oxide precursor composition; and
after removal of said portion of said alcohol, introducing a source of molybdenum into the mixture containing said solid vanadium/phosphorus oxide precursor compositions
incorporating molybdenum into the particulate vanadium/phosphorus oxide precursor, thereby forming a molybdenum-modified precursor composition;
removing alcohol to produce a dried solid molybdenum-modified precursor composition;
forming shaped bodies comprising said dried solid molybdenum-modified precursor composition; and
activating the dried formed molybdenum-modified precursor composition to transform into the active catalyst.

30. A fixed catalyst bed as set forth in claim 6 wherein said second catalyst zone comprises shaped bodies of phosphorus vanadium oxide catalyst having an individual catalyst body volume of at lout about 0.02 cc and a B.E.T. surface area of at least about 15 m.sup.2 /g.

31. A fixed catalyst bed gap adapted for the production of maleic anhydride by passage therethrough of a gas stream initially comprising a mixture of a nonaromatic hydrocarbon having at least four carbon atoms in a straight chain and an oxygen containing gas, said catalyst bed comprising:

a first zone containing a phosphorous vanadium oxide catalyst substantially devoid of active sites comprising molybdenum; and
second zone downstream of said first zone with respect to the flow of said gas stream, said second zone comprising shaped bodies of phosphorus vanadium oxide catalyst containing molybdenum in a molybdenum to phosphorus-ratio of between about 0.0020 and about 0.0060 and having an individual catalyst body volume of at least about 0.02 cc and a B.E.T. surface area of at least about 15 m.sup.2 /g.

32. A catalyst as set forth in claim 25 wherein the dried formed molybdenum-modified catalyst precursor composition is activated by the steps of:

(a) heating the dried formed molybdenum-modified catalyst precursor composition in an atmosphere selected from the group consisting of air, steam, inert gas, and mixtures thereof, to a temperature not to exceed 300.degree. C.;
(b) maintaining the dried formed molybdenum-modified catalyst precursor composition at the temperature of Step (a) and providing an atmosphere containing molecular oxygen, steam, and optionally an inert gas, the atmosphere being represented by the formula
(c) increasing the temperature of the dried formed molybdenum-modified catalyst precursor composition at a programmed rate of from about 2.degree. C./min to about 12.degree. C./min to a value effective to eliminate the water of hydration from the dried formed molybdenum-modified catalyst precursor composition;
(d) adjusting the temperature from Step (c) to a value greater than 350.degree. C., but less than 550.degree. C., and maintaining the adjusted temperature in the molecular oxygen/steam-containing atmosphere for a time effective to provide a vanadium oxidation state of from about +4.0 to about +4.5; and
(e) continuing to maintain the adjusted temperature in a nonoxidizing, steam-containing atmosphere for a time effective to complete the dried formed molybdenum-modified catalyst precursor composition to active catalyst transformation to yield the active catalyst.

33. An active catalyst as set forth in claim 24 wherein said mixture is heated to a reflux temperature ranging from about 90.degree. C. to about 120.degree. C. and maintained at the reflux temperature until said vanadium-containing compound is substantially exhausted by reaction with said pentavalent phosphorus- containing compound.

34. An active catalyst as set forth in claim 33 wherein the phosphorus containing compound and the vanadium- containing compound are reacted at a P/V ratio between about 1.05 and about 1.15.

35. An active catalyst as set forth in claim 24 wherein said mixture is cooled below about 50.degree. C. before introduction of the molybdenum-containing compound.

36. An active catalyst as set forth in claim 24 wherein said molybdenum-containing slurry is heated at a reflux temperature between about 90.degree. C. and about 120.degree. C.

37. An active catalyst as set forth in claim 24 wherein said molybdenum-containing compound is a slurry of a molybdenum-containing powder in a solvent.

38. An active catalyst as set forth in claim 24 wherein said molybdenum-containing compound is a molybdenum salt dissolved in a solvent.

39. An active catalyst as set forth in claim 25 wherein preparation of said catalyst further comprises heating a slurry containing molybdenum and said solid vanadium/phosphorus oxide precursor composition to effect incorporation of molybdenum and formation of a molybdenum-modified precursor composition.

40. An active catalyst as set forth in claim 25 wherein preparation of said catalyst further comprises settling said slurry such that said alcohol medium separates from said vanadium/phosphorus oxide precursor composition, and decanting said alcohol portion from said vanadium/phosphorus oxide precursor composition to provide a P/V ratio between about 1.055 and about 1.135.

41. An active catalyst as set forth in claim 40 wherein preparation of said catalyst further comprises stripping part of said alcohol medium from said slurry before said slurry is settled.

42. An active catalyst as set forth in claim 41 wherein preparation of said catalyst further comprises cooling said slurry before said slurry is settled.

43. An active catalyst as set forth in claim 42 wherein said slurry is cooled below about 50.degree. C.

44. An active catalyst as set forth in claim 39 wherein said molybdenum-containing slurry is heated at a reflux temperature between about 90.degree. C. and about 120.degree. C.

45. An active catalyst as set forth in claim 25 wherein said dried solid molybdenum-modified precursor composition corresponds to the formula:

46. An active catalyst as set forth in claim 26 wherein pores having a diameter between about 0.1 microns and about 3.3 microns constitute between about 25% and about 60% of the total pore volume of said active catalyst.

47. An active catalyst as set forth in claim 46 wherein pores having a diameter between about 0.1 microns (.mu.m) and about 3.3 microns constitute between about 30% and about 50% of the total pore volume of said active catalyst.

48. An active catalyst as set forth in claim 46 wherein pores having a diameter between about 0.2 and about 2.mu.m constitute between about 10% and about 40% of the total pore volume of the active catalyst, and pores having a diameter of between about 0.5 and about 1.2.mu.m constitute between about 5% and about 20% of the total pore volume.

49. An active catalyst as set forth in claim 48 wherein pores having a diameter between about 0.2 and about 2.mu.m constitute between about 12% and about 30% of the total pore volume of the active catalyst, and pores having a diameter of between about 0.5 and about 1.2.mu.m constitute between about 7% and about 12% of the total pore volume.

50. An active catalyst as set forth in claim 48 wherein pores having a diameter of less than about 0.1 microns constitute between about 40% and about 70% of the total pore volume of said active catalyst.

51. An active catalyst as set forth in claim 26 wherein said shaped body comprising said active catalyst has exit holes having a diameter of at least 2 microns at the external surfaces thereof, said holes being present in a density of at least about 75 surface holes per mm.sup.2, said holes being in communication with the body interior.

52. An active catalyst as set forth in claim 26 wherein said shaped body comprises an opening therethrough for flow of reactant and product gases when the active catalyst is used in the manufacture of maleic anhydride.

53. An active catalyst as set forth in claim 52 wherein said shaped body comprises a cylinder having a bore therethrough.

54. An catalyst as set forth in claim 27 wherein each of the shaped bodies comprising said catalyst has exit holes having a diameter of at least 2 microns at the external surfaces thereof, said holes being present in a density of at least about 100 surface holes per mm.sup.2, said holes being in communication with the body interior.

55. An active catalyst as set forth in claim 27 wherein the average oxidation state of the vanadium is between about 4.06 and about 4.30.

56. An active catalyst as set forth in claim 27 wherein pores having a diameter of greater than about 0.8 microns constitute at least about 8% of the total pore volume of said catalyst.

57. An active catalyst as set forth in claim 56 wherein pores having a diameter of greater than about 0.8 microns constitute between about 8% and about 50% of the total pore volume of said catalyst.

58. An active catalyst as set forth in claim 57 wherein pores having a diameter of greater than about 10 microns constitute between about 6% and about 40% of the total pore volume of said catalyst.

59. A process as set forth in claim 29 wherein said shaped bodies are formed by a process including the steps of:

forming a particulate phosphorus/vanadium oxide catalyst precursor composition from said dried solid molybdenum-modified precursor composition;
preparing a pore-modified catalyst precursor composition comprising a mixture of the particulate phosphorus/vanadium oxide catalyst precursor composition and a pore modification agent in proportions sufficient to provide a pore modification agent concentration of from about 4% to about 16% by weight, said pore modification agent being subject to vaporization, decomposition and/or oxidation at a temperature below 300.degree. C. without leaving a substantial residue;
forming said pore-modified catalyst precursor composition into a predetermined shape under compression, thereby producing said shaped bodies comprising said pore-modified catalyst precursor composition and containing said pore modification agent, said shaped bodies being porous; and
heating said shaped bodies while passing a stripping gas comprising air thereover for removal of at least about 80% by weight of said pore modification agent at a temperature not greater than about 300.degree. C., said shaped bodies being heated at a rate of between about 10 and about 3.degree. C. per minute to a hold temperature that is below a threshold temperature at which the pore modification agent is subject to catalytic oxidation in the presence of said pore-modified catalyst precursor composition, to form said dried formed solid molybdenum-modified precursor composition.

60. A process as set forth in claim 59 wherein said pore modification agent has a vapor pressure of at least about 1 mm Hg at a temperature between about 150.degree. C. and about 260.degree. C.

61. A process as set forth in claim 59 wherein the pore modification agent concentration of from about 8% to about 16% by weight.

62. A process as set forth in claim 60 wherein said shaped porous body is heated to a temperature between about 150.degree. C. and about 260.degree. C. for removal of said pore modification agent.

63. A process as set forth in claim 59 wherein the stripping gas flows over the precursor body at a linear rate of at least about 25 cm/sec.

64. A process as set forth in claim 59 wherein the stripping gas containing at least about 5% by volume water vapor when the temperature of said catalyst body is above the temperature at which the vapor pressure of the pore modification agent is 1 mm Hg.

65. A process as set forth in claim 64 wherein the stripping gas contains between about 20% and about 80% by volume water vapor when the temperature of said catalyst body is above the temperature at which said pore modification agent has a vapor pressure of 1 mm Hg.

66. A process as set forth in claim 59 wherein the composition of said stripping gas is such that no reaction that may occur between said agent and any component of said gas generates an exotherm sufficient to heat said body to a temperature of greater than 300.degree. C.

67. A process as set forth in claim 59 wherein oxygen is incorporated in said stripping gas so that, after 90% of said pore modification agent has been removed from said body, the proportion of oxygen in said gas is sufficient to prevent reduction of the average oxidation state of vanadium in said precursor body to less than about 3.8 but not sufficient to create a flammable mixture in said stripping gas.

68. A process as set forth in claim 63 wherein said pore modification agent substantially comprises stearic acid, and said hold temperature is between about 160.degree. C. and about 170.degree. C.

69. A process as set forth in claim 63 wherein said shaped bodies are heated from said hold temperature to a terminal temperature at which the concentration of residual pore modification agent in the shaped body has been reduced to a terminal level, the terminal level being defined as a concentration of residual pore modification agent which does not result in an exotherm that adversely alters the catalyst structure upon subsequent transformation of the dried formed molybdenum-modified catalyst precursor composition to active catalyst by heat treatment of said shaped bodies in the presence of air, steam or nitrogen under reference conditions, such reference conditions comprising heating said precursor at a rate of 1.8.degree. C. between 300.degree. C. and 400.degree. C.

70. A process as set forth in claim 69 wherein said shaped bodies are heated from said hold temperature at a rate of between about 0.5.degree. C. and about 2.degree. C. per hour in a temperature range between about 15.degree. C. and 40.degree. C. above the hold temperature.

71. A process as set forth in claim 70 wherein said shaped bodies are heated at a rate of between about 10.degree. C. and about 40.degree. C. per minute between a temperature of about 200.degree. C. and said terminal temperature.

72. A process as set forth in claim 71 wherein said terminal temperature is between about 240.degree. C. and about 260.degree. C.

73. A process as set forth in claim 72 wherein said shaped bodies are cooled from said terminal temperature to ambient temperature within about 0.5 to about 2 hours.

74. A process as set forth in claim 59 wherein said pore modification agent is removed by vaporization.

75. A process as set forth in claim 59 wherein said pore modification agent is recovered and reused in the preparation of further shaped bodies comprising said dried solid molybdenum-modified precursor composition.

76. A process as set forth in claim 74 wherein said pore modification agent has a vapor pressure of at least about 1 mm Hg at a temperature below 300.degree. C., and said pore modification agent is removed by passing a stripping gas over said shaped bodies at a temperature at which said vapor pressure is at least about 1 mm Hg.

77. A process as set forth in claim 59 wherein essentially complete removal of said pore modification agent is provided, without reduction of vanadium in said pore-modified catalyst precursor composition to an average oxidation state of less than about 3.8.

78. A process as set forth in claim 77 wherein said pore modification agent has a vapor pressure of at least about 1 mm Hg at a temperature below the temperature at which oxygen atoms in said pore-modified catalyst precursor composition are labile and subject to abstraction.

79. A process as set forth in claim 59 wherein said pore modification agent is selected from the group consisting of fatty acids, fatty acid esters, and polynuclear organic compounds.

80. A process as set forth in claim 59 wherein said pore modification agent is removed by oxidation or decomposition at a temperature below 300.degree. C.

81. A process as set forth in claim 59 wherein said particulate phosphorus/vanadium oxide catalyst precursor composition is mixed with a particulate pore modification agent, the mean particle diameter of said pore modification agent being not greater than about two orders of magnitude different from the mean particle diameter of said particulate phosphorus/vanadium oxide catalyst precursor composition.

82. A process as set forth in claim 81 wherein said pore modification agent has a mean particle diameter of between about 50 and about 2000 microns.

83. A process as set forth in claim 82 wherein said pore modification agent has a mean particle diameter of between about 100 and about 550 microns.

84. A process as set forth in claim 81 wherein said pore modification agent has a mean particle diameter of between about 10 and about 500 microns.

85. A process as set forth in claim 84 wherein said pore modification agent has a mean particle diameter of between about 30 and about 90 microns.

86. A process as set forth in claim 85 wherein said particulate phosphorus/vanadium oxide catalyst precursor composition has a mean particle diameter of between about 20 and about 200 microns.

87. A process as set forth in claim 59 wherein, after removal of said pore modification agent, said shaped bodies are heated at a temperature above 300.degree. C. to transform said shaped bodies to a phosphorus/vanadium oxide catalyst body active for the oxidation of a hydrocarbon to maleic anhydride.

88. A process as set forth in claim 59 wherein transformation of said dried formed molybdenum-modified catalyst precursor composition to said active catalyst comprises the steps of:

(a) heating said dried formed molybdenum-modified catalyst precursor composition in an atmosphere selected from the group consisting of air, steam, inert gas, and mixtures thereof to a temperature not to exceed about 300.degree. C., thereby removing said pore modification agent from said dried formed molybdenum-modified catalyst precursor composition substantially at a temperature below 300.degree. C.;
(b) maintaining the catalyst precursor body at the temperature of Step (a) and providing an atmosphere containing molecular oxygen, steam, and optionally an inert gas, the atmosphere being represented by the formula
(c) increasing the temperature of the catalyst precursor body at a programmed rate of from about 2.degree. C./min to about 12.degree. C./min to a value effective to eliminate the water of hydration from the catalyst precursor body;
(d) adjusting the temperature from Step (c) to a value greater than 350.degree. C., but less than 550.degree. C., and maintaining the adjusted temperature in the molecular oxygen/steam-containing atmosphere for a time effective to provide a vanadium oxidation state of from about +4.06 to about +4.3; and
(e) continuing to maintain the adjusted temperature in a nonoxidizing, steam-containing atmosphere for a time effective to complete the catalyst precursor body-to-active catalyst transformation to yield the active catalyst.

89. A process as set forth in claim 88 wherein transformation of said catalyst precursor body to said active catalyst is carried out after removal of said pore modification agent from said dried formed solid molybdenum-modified precursor composition.

90. A process as set forth in claim 88 wherein step (a) produces a catalyst precursor body having a pore volume of at least about 0.15 cc/g, at least about 25% of the pore volume of said catalyst precursor body being constituted of pores having a diameter between about 0.1 microns and about 3.3 microns, and at least about 40% of the pore volume being constituted of pores having a diameter of less than about 0.1 microns.

91. A process as set forth in claim 88 wherein step (a) produces a catalyst precursor body having a pore volume of at least about 0.15 cc/g, at least about 5% of the pore volume of said catalyst being constituted of pores having a diameter of at least about 0.8 microns, and at least about 4% of the pore volume being constituted of pores having a diameter of at least about 10 microns.

92. A process as set forth in claim 88 wherein said pore modification agent is removed during Step (c) of said transformation.

93. A process as set forth in claim 92 wherein oxygen in a proportion of between about 0.1 and about 1.5% by volume is included in said atmosphere during an initial heating period of between about 0.5 and about 10 hours, and thereafter the oxygen content of said atmosphere is increased to between about 2.0 and about 5% by volume.

94. A process as set forth in claim 93 wherein said atmosphere contains at least about 5% by volume water vapor when in said initial heating period the temperature of said catalyst body is above the temperature at which the vapor pressure of the pore modification agent is 1 mm Hg.

95. A process as set forth in claim 59 wherein said pore modification agent has a melting point of between about 35.degree. and about 100.degree. C., and a vapor pressure greater than 1 mm Hg at a temperature below 300.degree. C.

96. A process as set forth in claim 88 wherein said dried formed solid molybdenum-modified precursor composition is heated in the presence of said stripping gas until an end point at which at least about 80% of said pore modification agent has been removed from said catalyst precursor body, the terminal temperature of said catalyst body at said end point being at least 200.degree. C., and said catalyst precursor body is not cooled below about 100.degree. C. during the period after said end point and prior to Step (a) of the transformation of said catalyst precursor body to an active catalyst.

97. A process as set forth in claim 96 wherein said catalyst precursor body is not cooled by more than 50.degree. C. below said terminal temperature after said end point and prior to Step (a).

98. A process as set forth in claim 88 in which the pore modification agent is removed from said catalyst precursor body by passing said stripping gas over said catalyst precursor body in an oven, and transformation of said catalyst precursor body to active catalyst is carried out in the same oven without removal of the catalyst precursor body from the oven in the period between said end point and Step (a).

99. A process-as set forth in claim 28 wherein said mixture is cooled below about 50.degree. C. before introduction of the molybdenum-containing compound.

100. A process as set forth in claim 28 wherein said molybdenum-containing slurry is heated at a reflux temperature between about 90.degree. C. and about 120.degree. C.

101. A process as set forth in claim 28 wherein said molybdenum-containing compound is a slurry of a molybdenum-containing powder in a solvent.

102. A process as set forth in claim 28 wherein said molybdenum-containing compound is a molybdenum salt dissolved in a solvent.

103. A process as set forth in claim 28 wherein preparation of said catalyst further comprises heating a slurry containing molybdenum and said solid vanadium/phosphorus oxide precursor composition to effect incorporation of molybdenum and formation of a molybdenum-modified precursor composition.

104. A process as set forth in claim 28 wherein preparation of said catalyst further comprises settling said slurry such that said alcohol medium separates from said vanadium/phosphorus oxide precursor composition, and decanting said alcohol portion from said vanadium/phosphorus oxide precursor composition to provide a P/V ratio between about 1.055 and about 1.135.

105. A process as set forth in claim 104 wherein preparation of said catalyst further comprises stripping part of said alcohol medium from said slurry before said slurry is settled.

106. A process as set forth in claim 105 by wherein preparation of said catalyst further comprises cooling said slurry before said slurry is settled.

107. A process as set forth in claim 106 wherein said slurry is cooled below about 50.degree. C.

108. A process as set forth in claim 103 wherein said molybdenum-containing slurry is heated at a reflux temperature between about 90.degree. C. and about 120.degree. C.

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Patent History
Patent number: 5945368
Type: Grant
Filed: Oct 2, 1995
Date of Patent: Aug 31, 1999
Assignee: Huntsman Petrochemical Corporation (Salt Lake City, UT)
Inventors: Timothy R. Felthouse (St. Louis, MO), Robert A. Keppel (St. Louis, MO), Carl J. Schaefer (St. Louis, MO)
Primary Examiner: Michael Lewis
Assistant Examiner: Alexander G. Ghyka
Law Firm: Senniger Powers Leavitt & Roedel
Application Number: 8/538,005
Classifications
Current U.S. Class: And Vanadium Containing (502/209); Molybdenum (502/211); Of Group Vi (i.e., Cr, Mo, W Or Po) (502/305); Of Group V (i.e., V, Nb, Ta, As, Sb Or Bi) (502/353)
International Classification: B01J 27198; B01J 27199; B01J 2719;